That was a smart move. On Thursday, while he was out of town, I smelled gas and called PG&E again. They once again sent someone out - same fellow, it turns out - and while he was able to detect the gas as well he was unable to find a source. His best guess was that the 'off' valve was loose and a minute amount of gas was occasionally slipping through. He said it was non-hazardous, but it's never comforting to hear that there's a tiny gas leak in your home. He strongly replacing the wall unit as the one we have is old and frankly, a bit janky.
It was a cold couple of days with no heat. Luckily we live in California, where 'cold' is still well above freezing temperatures, but Sean and I were bundling up in fleece and thick sweaters and piles of blankets. Every night I pulled out a small space heater, loaned to us by a brother-in-law, and ran it for a couple of hours in the bedroom to raise the temperature of the room before going to sleep.
Today Papa Buckley rolled in to fix the heater. He and Sean discussed the matter and decided that a new wall unit was too costly (we were finding them for around $1000 online) so they replaced the gas valve and hose and voila! the leak was fixed. It was a pretty simple solution overall. It's lucky that this happened when Sean was of from work and able to make the repair quickly. If this had happened at the beginning of the month or in January, we'd probably have to wait a couple of weeks for everyone's schedule to align. Brrrr!